The present invention relates generally to a method and devices for applying the generally known principle of cascade flow in self-adjusting fluid handling systems, these devices being capable of maintaining pre-determined flow rate/pressure difference ratios over a wide range of variations. Thus, the applications, employed, e.g. in constant flow and contant pressure valves as described below, are two special cases only.
The invention further relates to fluid handling devices as mentioned above, which also are responsive to outside physical effects like temperature, pressure or electromagnetic force.
Furthermore, the invention relates to converting apparatus for measurement i.e. of flow rate, pressure and accumulated amount of thermal energy of fluid flow.
While the principal features of the invention are not limited in application to any particular fluid or fluid handling system, its desirable features and its attendant advantages are most apparent when applied in conjunctions with the control of draught in central heating boilers using solid fuel, in house ventilation system and for purposes of measurement.
Draught regulating systems for the control of combustion air in central heating boilers, which are small or medium in size, generally employ a bi-metal spiral spring or thermostat, which by means of a chain, closes the fire-door in case that the temperature of water in the system has reached the maximum allowed.
The system has the following defects:
It affects the primary air only, and there is no continuous control of secondary air. PA1 The action of the system has certain delay causing fluctuations in the process of combustion. PA1 The system is not responsive to variations in pressure difference in the flue, these variations being caused by variations in wind direction and pressure and by the temperature of the flue gases. PA1 A rather high pressure difference, 10 mm w.g. at least, is needed for accurate operation. PA1 Separate means of damping are necessary against pulsation effects of the duct system. PA1 Moving parts like the bearings and the damping mechanisms of the device are subject to impurities like dust and grease of the fluid. This has largely lowered functionality and accuracy of the devices. PA1 It is difficult to bring into effect adjustability of the device, particularly if automatic timing of the function is required. PA1 The device can not be made fireproof. PA1 It cannot be made adjustable. PA1 The impurities of the fluid like dust or grease in the air easily damage the functionality of the device. PA1 It is operational at very small difference of pressures. PA1 Its response to pressure variations is very rapid and accurate. PA1 It stabilizes the balance of said ventilation systems in case of occurence of said disturbances and rectifies erroneous design and leakages of the duct system. PA1 The apartment can be window-ventilated without any influence on ventilation and quality of air of other apartments. PA1 It enables adjustment of ventilation by individual spaces, which is essential for billing the heat consumption by apartments. PA1 The valve can replace separate fire shut-off valves between the fire compartments, if fitted with a thermofuse for fire shut-off release. PA1 The pneumatics applied forms a built-in system of damping against the pulsation effects of the duct system. PA1 No outside sources of power are needed for the operation. PA1 Because of its construction and way of function it is easy to fit the valve with remote-and-time control for purposes of energy saving. PA1 The method applied in the invention can be based either on vacuum or excess pressure of the fluid and serves, therefore, in systems both of supply and exhaust (suction). PA1 Only a fraction, about 1 percent, of the fluid flow is used for purposes of control and requires filtration. Therefore, all mechanical components of control and the moving parts as well work in a space of filtered air, which arrangement is essential both under habitable and industrial conditions.
The system described above is, in fact, a system of safety against boiling, not a system for maintaining constant draught as would be important in the boilers, particularly in care of installations having means for continuous feed of solid fuel.
The defects mentioned above can be avoided by means of an automatic butterfly valve in the flue, which is responsive to variations in the pressure of the flue gases and to the temperature of heating water. The outdoor temperature can also be considered in the regulation operation.
For this purpose, however, a complicated system with electronic and electromechanical components is necessary to control the movements of the flap and to overcome the resistance of the bearings and the stuffing boxes.
It is, therefore, desirable to provide an adjustable draught control device, which maintains selected constant draught between certain maximum and minimum values of the flue pressure, which is responsive to the temperature of water and which can be fitted with means for consideration of the indoor or outdoor temperatures in the regulation operation.
According to the present invention, there is provided a device, which is capable of maintaining a substantially constant draught in central heating boilers using solid fuel. This device is responsive even to small variations in flue pressure which are caused by variations in temperature of the flue gases, thermal height of the flue and variations in direction and pressure of winds. The temperatures of heating water and indoor or outdoor air can also be considered in the regulation operation.
A system of exhaust ventilation, based on common ventilator and main duct and fixed exhaust valves in each space, has become more and more general in blocks of flats because of its low cost in construction and maintenance.
A basic feature for the system is that the ventilator and the ducts are dimensioned to transfer constant volumes of air per hour from each space according to norms.
The exhaust valves are adjusted to a fixed position which can not be altered. In so doing, the volume flows of other valves and rates of ventilation in other spaces are affected. In addition, at lower pressures and rates of volume flow, the whole system or a part of it may get out of balance.
Therefore, the total rate of air exchange of an apartment depends on the needs of individual spaces like kitchen, WC and bathroom, and a total rate of air exchange of 1/hour or more in an apartment is quite common, whereas a rate of 0.5/h would be quite sufficient. This represents a large waste of energy in heating and the maintenance of humidity, not forgetting draughtiness and danger to health.
Opening the doors and windows affects the balance of the system causing also a mix of the ventilation air between the compartments.
The system is also exposed to disturbances caused by variations in natural draught and direction and pressure of winds. This in particular, when the revolutions of the ventilator, and the total volume flow respectively, drop down to 50% of normal for reasons of energy saving at lower outdoor temperatures. In this case, the pressure difference drops down to 25% of normal, which is less than the minimum for maintenance of the system balance.
It is, therefore, desirable to provide an adjustable, automatic exhaust valve, which maintains selected constant flow of air between pre-determined maximum and minimum values of the duct pressure. Moreover, the valve should be suitable for wall-mounting and be operational also at very low pressure differences, assumming there is no filtration of the main flow.
Automatic constant flow valves, capable of maintaining a constant volume flow rate, belong to the class of fluid flow regulators and have been disclosed in the prior art.
Devices are known, which employ linear or spiral springs and aerodynamic force of the liquid flow. These devices have the following disadvantages:
Furthermore, other devices are known, in which the constant rate of flow is maintained by an elastic bag in the opening of the main flow. The enclosure of the bag is connected, through a boring in its base, to the side of higher pressure, thus throttling the opening according to the variations in pressure difference.
Disadvantages of such devices are:
Constant flow values are also widely used, the function of which is based on use of outsider energy like electricity, pneumatics or hydraulics. Due to its complicated system, this type of valve is energy consuming and too expensive for control of ventilation in individual spaces of apartment buildings.
A reference can be made to U.S. Pat. No. 4,121,762, showing an automatic fluid flow regulator. The regulator described belongs to the group of devices employing (a group of) linear springs and aerodynamic force of the fluid flow.
In addition, a pneumatic, thermometric mechanism may also be employed to adjust the flow in response to changes in temperature and independent of pressure variations.
The system described shares the disadvantages of this group of devices as given above, excluding, however, damping of pulsations. Furthermore, it is not suitable for wall-mounting in habitable spaces and it presumes both very high pressure difference and full filtration of the main flow for proposed function.